Various types of hearing prostheses provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, and/or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, such as in the cochlea where sound or acoustic vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with some forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing devices. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sound into the person's ear. Vibration-based hearing devices typically include a small microphone to detect sound and a vibration mechanism to apply vibrations, which represent the detected sound, directly or indirectly to a person's bone or teeth, thereby causing vibrations in the person's inner ear and bypassing the person's auditory canal and middle ear.
Vibration-based hearing devices include, for example, bone conduction devices, direct acoustic cochlear stimulation devices, and other vibration-based devices. A bone conduction device typically utilizes a surgically implanted mechanism or a passive connection through the skin or teeth to transmit vibrations via the skull. Similarly, a direct acoustic cochlear stimulation device typically utilizes a surgically implanted mechanism to transmit vibrations, but bypasses the skull and more directly stimulates the inner ear. Other vibration-based hearing devices may use similar vibration mechanisms to transmit acoustic signals via direct or indirect vibration applied to teeth or other cranial or facial structures.
Persons with certain forms of sensorineural hearing loss may benefit from implanted prostheses, such as cochlear implants and/or auditory brainstem implants. Generally, cochlear implants and auditory brainstem implants electrically stimulate auditory nerves in the cochlea or the brainstem to enable persons with sensorineural hearing loss to perceive sound. For example, a cochlear implant uses a small microphone to convert sound into a series of electrical signals, and uses the series of electrical signals to stimulate the auditory nerve of the recipient via an array of electrodes implanted in the cochlea. An auditory brainstem implant can use technology similar to cochlear implants, but instead of applying electrical stimulation to a person's cochlea, the auditory brainstem implant applies electrical stimulation directly to a person's brainstem, bypassing the cochlea altogether.
In addition, some persons may benefit from a bimodal hearing prosthesis that combines one or more characteristics of acoustic hearing aids, vibration-based hearing devices, cochlear implants, or auditory brainstem implants to enable the person to perceive sound.